/*
 * Copyright (c) 1998, 2004, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/* __ieee754_pow(x,y) return x**y
 *
 *                    n
 * Method:  Let x =  2   * (1+f)
 *      1. Compute and return log2(x) in two pieces:
 *              log2(x) = w1 + w2,
 *         where w1 has 53-24 = 29 bit trailing zeros.
 *      2. Perform y*log2(x) = n+y' by simulating muti-precision
 *         arithmetic, where |y'|<=0.5.
 *      3. Return x**y = 2**n*exp(y'*log2)
 *
 * Special cases:
 *      1.  (anything) ** 0  is 1
 *      2.  (anything) ** 1  is itself
 *      3.  (anything) ** NAN is NAN
 *      4.  NAN ** (anything except 0) is NAN
 *      5.  +-(|x| > 1) **  +INF is +INF
 *      6.  +-(|x| > 1) **  -INF is +0
 *      7.  +-(|x| < 1) **  +INF is +0
 *      8.  +-(|x| < 1) **  -INF is +INF
 *      9.  +-1         ** +-INF is NAN
 *      10. +0 ** (+anything except 0, NAN)               is +0
 *      11. -0 ** (+anything except 0, NAN, odd integer)  is +0
 *      12. +0 ** (-anything except 0, NAN)               is +INF
 *      13. -0 ** (-anything except 0, NAN, odd integer)  is +INF
 *      14. -0 ** (odd integer) = -( +0 ** (odd integer) )
 *      15. +INF ** (+anything except 0,NAN) is +INF
 *      16. +INF ** (-anything except 0,NAN) is +0
 *      17. -INF ** (anything)  = -0 ** (-anything)
 *      18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)
 *      19. (-anything except 0 and inf) ** (non-integer) is NAN
 *
 * Accuracy:
 *      pow(x,y) returns x**y nearly rounded. In particular
 *                      pow(integer,integer)
 *      always returns the correct integer provided it is
 *      representable.
 *
 * Constants :
 * The hexadecimal values are the intended ones for the following
 * constants. The decimal values may be used, provided that the
 * compiler will convert from decimal to binary accurately enough
 * to produce the hexadecimal values shown.
 */
using unsigned = System.UInt32;
#pragma warning disable 168

namespace IKVM.Runtime.Util.Java.Lang
{
    static partial class fdlibm
    {
        static readonly double[] bp = { 1.0, 1.5, };
        static readonly double[] dp_h = { 0.0, 5.84962487220764160156e-01, }; /* 0x3FE2B803, 0x40000000 */
        static readonly double[] dp_l = { 0.0, 1.35003920212974897128e-08, }; /* 0x3E4CFDEB, 0x43CFD006 */

        internal static double __ieee754_pow(double x, double y)
        {
            const double zero = 0.0,
    one = 1.0,
    two = 2.0,
    two53 = 9007199254740992.0,  /* 0x43400000, 0x00000000 */
    huge = 1.0e300,
    tiny = 1.0e-300,
    /* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
    L1 = 5.99999999999994648725e-01, /* 0x3FE33333, 0x33333303 */
    L2 = 4.28571428578550184252e-01, /* 0x3FDB6DB6, 0xDB6FABFF */
    L3 = 3.33333329818377432918e-01, /* 0x3FD55555, 0x518F264D */
    L4 = 2.72728123808534006489e-01, /* 0x3FD17460, 0xA91D4101 */
    L5 = 2.30660745775561754067e-01, /* 0x3FCD864A, 0x93C9DB65 */
    L6 = 2.06975017800338417784e-01, /* 0x3FCA7E28, 0x4A454EEF */
    P1 = 1.66666666666666019037e-01, /* 0x3FC55555, 0x5555553E */
    P2 = -2.77777777770155933842e-03, /* 0xBF66C16C, 0x16BEBD93 */
    P3 = 6.61375632143793436117e-05, /* 0x3F11566A, 0xAF25DE2C */
    P4 = -1.65339022054652515390e-06, /* 0xBEBBBD41, 0xC5D26BF1 */
    P5 = 4.13813679705723846039e-08, /* 0x3E663769, 0x72BEA4D0 */
    lg2 = 6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
    lg2_h = 6.93147182464599609375e-01, /* 0x3FE62E43, 0x00000000 */
    lg2_l = -1.90465429995776804525e-09, /* 0xBE205C61, 0x0CA86C39 */
    ovt = 8.0085662595372944372e-0017, /* -(1024-log2(ovfl+.5ulp)) */
    cp = 9.61796693925975554329e-01, /* 0x3FEEC709, 0xDC3A03FD =2/(3ln2) */
    cp_h = 9.61796700954437255859e-01, /* 0x3FEEC709, 0xE0000000 =(float)cp */
    cp_l = -7.02846165095275826516e-09, /* 0xBE3E2FE0, 0x145B01F5 =tail of cp_h*/
    ivln2 = 1.44269504088896338700e+00, /* 0x3FF71547, 0x652B82FE =1/ln2 */
    ivln2_h = 1.44269502162933349609e+00, /* 0x3FF71547, 0x60000000 =24b 1/ln2*/
    ivln2_l = 1.92596299112661746887e-08; /* 0x3E54AE0B, 0xF85DDF44 =1/ln2 tail*/

            double z, ax, z_h, z_l, p_h, p_l;
            double y1, t1, t2, r, s, t, u, v, w;
            int i0, i1, i, j, k, yisint, n;
            int hx, hy, ix, iy;
            unsigned lx, ly;

            hx = __HI(x); lx = (uint)__LO(x);
            hy = __HI(y); ly = (uint)__LO(y);
            ix = hx & 0x7fffffff; iy = hy & 0x7fffffff;

            /* y==zero: x**0 = 1 */
            if ((iy | (int)ly) == 0) return one;

            /* +-NaN return x+y */
            if (ix > 0x7ff00000 || ((ix == 0x7ff00000) && (lx != 0)) ||
               iy > 0x7ff00000 || ((iy == 0x7ff00000) && (ly != 0)))
                return x + y;

            /* determine if y is an odd int when x < 0
             * yisint = 0       ... y is not an integer
             * yisint = 1       ... y is an odd int
             * yisint = 2       ... y is an even int
             */
            yisint = 0;
            if (hx < 0)
            {
                if (iy >= 0x43400000) yisint = 2; /* even integer y */
                else if (iy >= 0x3ff00000)
                {
                    k = (iy >> 20) - 0x3ff;        /* exponent */
                    if (k > 20)
                    {
                        j = (int)(ly >> (52 - k));
                        if ((j << (52 - k)) == (int)ly) yisint = 2 - (j & 1);
                    }
                    else if (ly == 0)
                    {
                        j = iy >> (20 - k);
                        if ((j << (20 - k)) == iy) yisint = 2 - (j & 1);
                    }
                }
            }

            /* special value of y */
            if (ly == 0)
            {
                if (iy == 0x7ff00000)
                {       /* y is +-inf */
                    if (((ix - 0x3ff00000) | (int)lx) == 0)
                        return y - y;      /* inf**+-1 is NaN */
                    else if (ix >= 0x3ff00000)/* (|x|>1)**+-inf = inf,0 */
                        return (hy >= 0) ? y : zero;
                    else                    /* (|x|<1)**-,+inf = inf,0 */
                        return (hy < 0) ? -y : zero;
                }
                if (iy == 0x3ff00000)
                {        /* y is  +-1 */
                    if (hy < 0) return one / x; else return x;
                }
                if (hy == 0x40000000) return x * x; /* y is  2 */
                if (hy == 0x3fe00000)
                {        /* y is  0.5 */
                    if (hx >= 0)       /* x >= +0 */
                        return sqrt(x);
                }
            }

            ax = fabs(x);
            /* special value of x */
            if (lx == 0)
            {
                if (ix == 0x7ff00000 || ix == 0 || ix == 0x3ff00000)
                {
                    z = ax;                 /*x is +-0,+-inf,+-1*/
                    if (hy < 0) z = one / z;     /* z = (1/|x|) */
                    if (hx < 0)
                    {
                        if (((ix - 0x3ff00000) | yisint) == 0)
                        {
                            z = (z - z) / (z - z); /* (-1)**non-int is NaN */
                        }
                        else if (yisint == 1)
                            z = -1.0 * z;             /* (x<0)**odd = -(|x|**odd) */
                    }
                    return z;
                }
            }

            n = (hx >> 31) + 1;

            /* (x<0)**(non-int) is NaN */
            if ((n | yisint) == 0) return (x - x) / (x - x);

            s = one; /* s (sign of result -ve**odd) = -1 else = 1 */
            if ((n | (yisint - 1)) == 0) s = -one;/* (-ve)**(odd int) */

            /* |y| is huge */
            if (iy > 0x41e00000)
            { /* if |y| > 2**31 */
                if (iy > 0x43f00000)
                {  /* if |y| > 2**64, must o/uflow */
                    if (ix <= 0x3fefffff) return (hy < 0) ? huge * huge : tiny * tiny;
                    if (ix >= 0x3ff00000) return (hy > 0) ? huge * huge : tiny * tiny;
                }
                /* over/underflow if x is not close to one */
                if (ix < 0x3fefffff) return (hy < 0) ? s * huge * huge : s * tiny * tiny;
                if (ix > 0x3ff00000) return (hy > 0) ? s * huge * huge : s * tiny * tiny;
                /* now |1-x| is tiny <= 2**-20, suffice to compute
                   log(x) by x-x^2/2+x^3/3-x^4/4 */
                t = ax - one;         /* t has 20 trailing zeros */
                w = (t * t) * (0.5 - t * (0.3333333333333333333333 - t * 0.25));
                u = ivln2_h * t;      /* ivln2_h has 21 sig. bits */
                v = t * ivln2_l - w * ivln2;
                t1 = u + v;
                t1 = __LO(t1, 0);
                t2 = v - (t1 - u);
            }
            else
            {
                double ss, s2, s_h, s_l, t_h, t_l;
                n = 0;
                /* take care subnormal number */
                if (ix < 0x00100000)
                { ax *= two53; n -= 53; ix = __HI(ax); }
                n += ((ix) >> 20) - 0x3ff;
                j = ix & 0x000fffff;
                /* determine interval */
                ix = j | 0x3ff00000;          /* normalize ix */
                if (j <= 0x3988E) k = 0;         /* |x|<sqrt(3/2) */
                else if (j < 0xBB67A) k = 1;     /* |x|<sqrt(3)   */
                else { k = 0; n += 1; ix -= 0x00100000; }
                ax = __HI(ax, ix);

                /* compute ss = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
                u = ax - bp[k];               /* bp[0]=1.0, bp[1]=1.5 */
                v = one / (ax + bp[k]);
                ss = u * v;
                s_h = ss;
                s_h = __LO(s_h, 0);
                /* t_h=ax+bp[k] High */
                t_h = zero;
                t_h = __HI(t_h, ((ix >> 1) | 0x20000000) + 0x00080000 + (k << 18));
                t_l = ax - (t_h - bp[k]);
                s_l = v * ((u - s_h * t_h) - s_h * t_l);
                /* compute log(ax) */
                s2 = ss * ss;
                r = s2 * s2 * (L1 + s2 * (L2 + s2 * (L3 + s2 * (L4 + s2 * (L5 + s2 * L6)))));
                r += s_l * (s_h + ss);
                s2 = s_h * s_h;
                t_h = 3.0 + s2 + r;
                t_h = __LO(t_h, 0);
                t_l = r - ((t_h - 3.0) - s2);
                /* u+v = ss*(1+...) */
                u = s_h * t_h;
                v = s_l * t_h + t_l * ss;
                /* 2/(3log2)*(ss+...) */
                p_h = u + v;
                p_h = __LO(p_h, 0);
                p_l = v - (p_h - u);
                z_h = cp_h * p_h;             /* cp_h+cp_l = 2/(3*log2) */
                z_l = cp_l * p_h + p_l * cp + dp_l[k];
                /* log2(ax) = (ss+..)*2/(3*log2) = n + dp_h + z_h + z_l */
                t = (double)n;
                t1 = (((z_h + z_l) + dp_h[k]) + t);
                t1 = __LO(t1, 0);
                t2 = z_l - (((t1 - t) - dp_h[k]) - z_h);
            }

            /* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
            y1 = y;
            y1 = __LO(y1, 0);
            p_l = (y - y1) * t1 + y * t2;
            p_h = y1 * t1;
            z = p_l + p_h;
            j = __HI(z);
            i = __LO(z);
            if (j >= 0x40900000)
            {                            /* z >= 1024 */
                if (((j - 0x40900000) | i) != 0)                   /* if z > 1024 */
                    return s * huge * huge;                     /* overflow */
                else
                {
                    if (p_l + ovt > z - p_h) return s * huge * huge;   /* overflow */
                }
            }
            else if ((j & 0x7fffffff) >= 0x4090cc00)
            {        /* z <= -1075 */
                if (((int)(j - 0xc090cc00) | i) != 0)           /* z < -1075 */
                    return s * tiny * tiny;             /* underflow */
                else
                {
                    if (p_l <= z - p_h) return s * tiny * tiny;      /* underflow */
                }
            }
            /*
             * compute 2**(p_h+p_l)
             */
            i = j & 0x7fffffff;
            k = (i >> 20) - 0x3ff;
            n = 0;
            if (i > 0x3fe00000)
            {              /* if |z| > 0.5, set n = [z+0.5] */
                n = j + (0x00100000 >> (k + 1));
                k = ((n & 0x7fffffff) >> 20) - 0x3ff;     /* new k for n */
                t = zero;
                t = __HI(t, (n & ~(0x000fffff >> k)));
                n = ((n & 0x000fffff) | 0x00100000) >> (20 - k);
                if (j < 0) n = -n;
                p_h -= t;
            }
            t = p_l + p_h;
            t = __LO(t, 0);
            u = t * lg2_h;
            v = (p_l - (t - p_h)) * lg2 + t * lg2_l;
            z = u + v;
            w = v - (z - u);
            t = z * z;
            t1 = z - t * (P1 + t * (P2 + t * (P3 + t * (P4 + t * P5))));
            r = (z * t1) / (t1 - two) - (w + z * w);
            z = one - (r - z);
            j = __HI(z);
            j += (n << 20);
            if ((j >> 20) <= 0) z = scalbn(z, n); /* subnormal output */
            else z = __HI(z, __HI(z) + (n << 20));
            return s * z;
        }
    }
}